New perspectives on Ganymede.

Calling all hot doggers! Take a gander at these steep, frosted slopes that shoot into icy craters (top). This view of a northern patch of Jupiter's moon Ganymede reveals what may be the best place to schuss and slalom on the solar system's biggest satellite.

Taken by the Galileo spacecraft during a Sept. 6 flyby, this image poses a puzzle. Although the sun shines from the south, the north-facing walls of the ridges and craters are brighter than the south-facing ones. James W. Head, a member of the Galileo imaging team at Brown University in Providence, R.I., suggests that the pattern tracks the migration of ice. He and other scientists propose that the chillier north-facing walls trap water-ice vaporized from the sun-warmed, southern slopes. A deposit of frost would explain the brightness of the northern faces.

"The evidence really points out that sublimation and redeposition [of water-ice] is an important process on Ganymede and perhaps other icy satellites," Head says. Scientists have also created a three-dimensional image (bottom) of Ganymede's rugged Galileo Regio region by combining images taken June 27 and Sept. 6, when the Galileo craft flew past the same site at different viewing angles. With this stereo perspective, "you get a real sense of the personality of the landscape," including the heights of raised rims and the depths of furrows and impact craters, Head notes. In other images, showing the Nippur Sulcus region, scientists see Ganymede's darker, presumably older terrain blending into brighter, younger terrain. Faulting appears to be chopping up the older surface. "You see the process in action," notes John R. Spencer of Lowell Observatory in Flagstaff, Ariz.

These and other Galileo pictures, only recently radioed to Earth, were unveiled last week at the annual meeting of the American Astronomical Society's Division of Planetary Sciences in Tucson.